The invention relates to a method and a control system for distance and speed control of a vehicle according to the preamble of Claims 1 and 16, respectively.
The printed publication German Patent DE 44 07 082 A1 discloses a vehicle speed control system for setting the speed of a vehicle following a vehicle driving in front. Actuating signals for adjusting the transmission and the throttle are generated, as a function of the distance and the relative speed, in a regulation and control unit of the system in order to influence the torque which can be transmitted onto the road, as a result of which the distance between the controlled vehicle and the vehicle driving in front can be regulated.
The generically determinative printed publication German Patent DE 43 28 304 A1 discloses a control system for an automatic brake for an automobile, which has a measuring device for determining the relative distance between the leading vehicle and the following vehicle, and for measuring the speeds of both vehicles. On the basis of these measured values, a statement on whether there is a risk of collision between the following vehicle and the leading vehicle is made in a computing unit of the control system in accordance with a stored combinatorial rule. In this case, a desired deceleration is determined for the following vehicle and is converted into a corresponding brake pressure for braking the vehicle, in order to prevent a collision between the vehicles.
The problem on which this invention is based is to set the distance and/or the relative speed of a following vehicle in relation to a vehicle driving in front in a controlled fashion.
This problem is solved according to the invention with the aid of the features of Claims 1 and 16, respectively.
It is provided in accordance with the innovation that firstly, as a function of the distance between the vehicles and/or the speed difference, a desired deceleration is determined which the following vehicle is to run through in order to preserve a predetermined distance and/or to reserve a permitted speed difference. However, the desired deceleration is converted into an automatic braking operation only if the absolute value of the desired deceleration overshoots a threshold value which is fixed as a positive value. The introduction of a threshold value, and the comparison of the calculated desired deceleration with the threshold value ensure that the automatic actuation of the vehicle brake, and the higher vehicle deceleration associated therewith are carried out only in those cases in which adaptation of the speed and/or the distance cannot be realized, or can be realized only with insufficient reliability using other means. The value of the desired deceleration offers a reliable indication for deciding whether automatic actuation of the vehicle brake is required.
A further advantage of this method resides in the fact that the automatic actuation of the vehicle brake can be cancelled at any time as soon as a condition that the absolute value of the desired deceleration overshoots an associated threshold value is no longer fulfilled, with the result that the desired deceleration required for braking the vehicle can be achieved with other means which exhibit a softer braking response with a higher degree comfort. The harder braking response by actuating the vehicle brake is reserved for the critical situations.
For the case when the absolute value of the desired deceleration is below the threshold value, it is expedient for the vehicle deceleration to be implemented via transmission intervention and/or engine torque intervention. Such vehicle interventions, for example automated changing down into a lower gear, automated interventions in the throttle position or influencing of the fuel injection, can be carried out using already existing speed and distance control systems which can advantageously be incorporated into the novel control system.
For the case in which an automatic braking operation is required because of overshooting of the threshold value, the braking operation is preferably to be maintained until a limit value of the cyclically determined desired deceleration has been reached, the limit value being smaller in absolute value than the threshold value, with the result that the automatic braking operation for braking the vehicle to a lower speed is firstly maintained, and subsequently a further deceleration is carried out, for example by transmission interventions or engine torque interventions.
The desired deceleration is advantageously calculated as a function of the vehicle distance, the differential speed and the change in speed of the vehicle driving in front. The speed difference preferably features quadratically in the calculation of the desired deceleration, and thereby experiences a stronger weighting. The change in speed of the leading vehicle expediently enters linearly into the computer rule for the desired deceleration, whereas the vehicle distance enters. reciprocally, in order to ensure that small distances result in a high vehicle deceleration.
In a preferred development, it is provided that, for the case in which the vehicle distance undershoots a lower limit value, the desired deceleration is set to a constant maximum value which is above the values of the desired deceleration determined using the computing rule. The aim is to ensure thereby that in the case of relatively small vehicle distances the vehicle deceleration is set to a maximum value in order to brake the vehicle as quickly as possible and to enlarge the vehicle distance. The lower vehicle distance limit value is a function, in particular, of the speed of the leading vehicle, a linear relationship preferably being selected such that with increasing speed of the leading vehicle the lower limit value rises proportionally.
The automatic actuation of the vehicle brake is advantageously performed independently of a brake actuation produced by the driver, in order to ensure that in the case of an inadequate brake actuation by the driver the required vehicle deceleration can automatically be achieved via the control system. For this design, in particular, already existing braking assistance systems can be integrated into the control system according to the invention in addition, or as an alternative to distance control and/or speed control systems.
Further advantages and expedient embodiments may be gathered from the description of the figures and the drawing, which illustrates a flowchart with the method steps for a control system according to the invention for distance and speed control of a vehicle.